This is a Shannon Award providing partial support for the research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon Award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. The abstract below is taken from the original document submitted by the principal investigator. It is becoming increasingly apparent that the genetic events that occur in the genesis of many cancers involves not only alterations in growth regulatory pathways but also alterations in the programmed cell death (apoptosis) pathway present in normal cells. These alterations involve the p53, c-myc, and bcl-2 genes. Recent observations implicate that changes in these genes may also be responsible for resistance of cancer cells to therapy-induced apoptosis. This and other laboratories has shown that during the G1 phase of the cell cycle p53 can induce apoptosis in some cell lines and cell cycle arrest in others. This laboratory has also found that in mouse erythroleukemia (MEL) cells deregulated expression of bcl-2 and c-myc totally abrogates p53 growth suppression. c-myc and bcl-2 alter the subcellular trafficking of p53 during the cell cycle: the p53 remains in the cytoplasm of the co-transfected cells during G1 when they are susceptible to p53-induced death. This finding suggests a mechanism by which normal hematopoietic progenitors can survive and proliferate despite p53 expression and by which the inappropriate expression of bcl-2 and c-myc can cooperate in transformation. Supporting this as a more general mechanism by which cancer cells escape p53-induced growth suppression, MCF-7 breast cancer cell line (which express wild type p53 and high levels of bcl-2 and c- myc) transduced with a dominant-negative bcl-2 minigene rapidly lose viability. Taken together, these data suggests that the oncogene bcl-2 allows cells to escape p53-induced apoptosis, while the oncogene c-myc overcomes p53-induced cell cycle arrest. Based on this hypothesis, we propose to use a molecular approach to target these pathways in order to enhance the ability of radiation to induce apoptosis. To further define the functional interaction of bcl-2, c-myc, and, strategies to express c-myc with p53 and to inhibit bcl-2 function in breast cancer cells will be developed. The following specific aims are designed to achieve this goal. First to confirm that the deregulated expression of bcl-2, and c- myc is a mechanism by which some cancer cells, such as breast and colon cancer cells, overcome p53 anti-proliferative effects. Second, to further characterize the subcellular localization of p53 during the cell cycle in cells which co-express bcl-2 and c-myc. Third, to identify the cis-acting sequences which determine p53 compartmentalization during the cell cycle. Fourth, to determine whether Bcl-2 and Myc regulate the conformation of p53 during the cell cycle. Fifth, and finally, to determine whether p53 synthesized during G1 in cells expressing c-myc and bcl-2 is able to translocate into the nucleus when cells enter S phase. These studies will give insight into the molecular mechanism by Bcl-2 and Myc modulate p53 functions.